1. Field of the Invention
The present invention relates to camera exposure control devices capable of measuring light reflected from the surfaces of a leading shutter curtain and a film for exposure control based on the light measurement, and more particularly to such exposure control devices which provide correction of the exposure control to account for the differences in reflectivity between the surface of the leading shutter curtain and the film surface.
2. Description of the Prior Art
With some prior art exposure control devices of the above described type, the surface of the leading shutter curtain (facing an objective) is adapted to have a given reflecting power with the assumption that reflecting powers of the surfaces (the emulsion surfaces) of films are common and identical to the given reflecting power regardless of the types of the films. In fact, however, the surfaces of different type films have different reflecting powers and even the surfaces of the same type films may represent different reflecting powers. Thus, even if the scene brightness and the aperture size of an objective remains unchanged for each light measurement, the intensity of the scene light incident on a light receiving element after having been reflected from the surface of the film will become different in accordance with the film in use, resulting in different light measurement.
With the prior art exposure control device of this type, therefore, when the reflecting power of the surface of the film is actually higher than that of the surface of the leading shutter curtain under conditions of the same scene brightness and aperture size, the intensity of the scene light incident on the light receiving element increases after the start of travel of the leading shutter curtain, whereby the shutter is controlled at an exposure time shorter than the correct exposure time, resulting in an underexposure. In contrast thereto, when the reflecting power of the surface of the film is lower than that of the surface of the leading shutter curtain, the intensity of the scene light incident on the light receiving element decreases after the start of travel of the leading shutter curtain travel, whereby the shutter is controlled at an exposure time longer than the correct exposure time, resulting in an overexposure.
To solve the above problem, there have been proposed exposure control devices which, besides the light receiving element capable of measuring light, reflected from the surfaces of a leading shutter curtain and a film, for exposure control, include a second light receiving element arranged for detecting the difference in reflecting power between the surfaces of the leading shutter curtain and the film to thereby correct any exposure error in accordance with the difference thus detected.
However, the exposure control devices of this type have the disadvantages of an increase in the number of components and the cost of manufacturing because they additionally and necessarily require not only the second light receiving element but also lead wires connected to the second light receiving element and a condenser lens disposed in front of the second light receiving element.